Update alignment section
[ctf.git] / common-trace-format-proposal.txt
1
2 RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
3
4 Mathieu Desnoyers, EfficiOS Inc.
5
6 The goal of the present document is to propose a trace format that suits the
7 needs of the embedded, telecom, high-performance and kernel communities. It is
8 based on the Common Trace Format Requirements (v1.4) document. It is designed to
9 allow traces to be natively generated by the Linux kernel, Linux user-space
10 applications written in C/C++, and hardware components.
11
12 The latest version of this document can be found at:
13
14 git tree: git://git.efficios.com/ctf.git
15 gitweb: http://git.efficios.com/?p=ctf.git
16
17 A reference implementation of a library to read and write this trace format is
18 being implemented within the BabelTrace project, a converter between trace
19 formats. The development tree is available at:
20
21 git tree: git://git.efficios.com/babeltrace.git
22 gitweb: http://git.efficios.com/?p=babeltrace.git
23
24
25 1. Preliminary definitions
26
27 - Event Trace: An ordered sequence of events.
28 - Event Stream: An ordered sequence of events, containing a subset of the
29 trace event types.
30 - Event Packet: A sequence of physically contiguous events within an event
31 stream.
32 - Event: This is the basic entry in a trace. (aka: a trace record).
33 - An event identifier (ID) relates to the class (a type) of event within
34 an event stream.
35 e.g. event: irq_entry.
36 - An event (or event record) relates to a specific instance of an event
37 class.
38 e.g. event: irq_entry, at time X, on CPU Y
39 - Source Architecture: Architecture writing the trace.
40 - Reader Architecture: Architecture reading the trace.
41
42
43 2. High-level representation of a trace
44
45 A trace is divided into multiple event streams. Each event stream contains a
46 subset of the trace event types.
47
48 The final output of the trace, after its generation and optional transport over
49 the network, is expected to be either on permanent or temporary storage in a
50 virtual file system. Because each event stream is appended to while a trace is
51 being recorded, each is associated with a separate file for output. Therefore,
52 a stored trace can be represented as a directory containing one file per stream.
53
54 A metadata event stream contains information on trace event types. It describes:
55
56 - Trace version.
57 - Types available.
58 - Per-stream event header description.
59 - Per-stream event header selection.
60 - Per-stream event context fields.
61 - Per-event
62 - Event type to stream mapping.
63 - Event type to name mapping.
64 - Event type to ID mapping.
65 - Event fields description.
66
67
68 3. Event stream
69
70 An event stream is divided in contiguous event packets of variable size. These
71 subdivisions have a variable size. An event packet can contain a certain
72 amount of padding at the end. The stream header is repeated at the
73 beginning of each event packet. The rationale for the event stream
74 design choices is explained in Appendix B. Stream Header Rationale.
75
76 The event stream header will therefore be referred to as the "event packet
77 header" throughout the rest of this document.
78
79
80 4. Types
81
82 Types are organized as type classes. Each type class belong to either of two
83 kind of types: basic types or compound types.
84
85 4.1 Basic types
86
87 A basic type is a scalar type, as described in this section. It includes
88 integers, GNU/C bitfields, enumerations, and floating point values.
89
90 4.1.1 Type inheritance
91
92 Type specifications can be inherited to allow deriving types from a
93 type class. For example, see the uint32_t named type derived from the "integer"
94 type class below ("Integers" section). Types have a precise binary
95 representation in the trace. A type class has methods to read and write these
96 types, but must be derived into a type to be usable in an event field.
97
98 4.1.2 Alignment
99
100 We define "byte-packed" types as aligned on the byte size, namely 8-bit.
101 We define "bit-packed" types as following on the next bit, as defined by the
102 "Integers" section.
103
104 All basic types, except bitfields, are either aligned on an architecture-defined
105 specific alignment or byte-packed, depending on the architecture preference.
106 Architectures providing fast unaligned write byte-packed basic types to save
107 space, aligning each type on byte boundaries (8-bit). Architectures with slow
108 unaligned writes align types on specific alignment values. If no specific
109 alignment is declared for a type, it is assumed to be bit-packed for
110 integers with size not multiple of 8 bits and for gcc bitfields. All
111 other types are byte-packed.
112
113 Metadata attribute representation of a specific alignment:
114
115 align = value; /* value in bits */
116
117 4.1.3 Byte order
118
119 By default, the native endianness of the source architecture the trace is used.
120 Byte order can be overridden for a basic type by specifying a "byte_order"
121 attribute. Typical use-case is to specify the network byte order (big endian:
122 "be") to save data captured from the network into the trace without conversion.
123 If not specified, the byte order is native.
124
125 Metadata representation:
126
127 byte_order = native OR network OR be OR le; /* network and be are aliases */
128
129 4.1.4 Size
130
131 Type size, in bits, for integers and floats is that returned by "sizeof()" in C
132 multiplied by CHAR_BIT.
133 We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
134 to 8 bits for cross-endianness compatibility.
135
136 Metadata representation:
137
138 size = value; (value is in bits)
139
140 4.1.5 Integers
141
142 Signed integers are represented in two-complement. Integer alignment, size,
143 signedness and byte ordering are defined in the metadata. Integers aligned on
144 byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
145 the C99 standard integers. In addition, integers with alignment and/or size that
146 are _not_ a multiple of the byte size are permitted; these correspond to the C99
147 standard bitfields, with the added specification that the CTF integer bitfields
148 have a fixed binary representation. A MIT-licensed reference implementation of
149 the CTF portable bitfields is available at:
150
151 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
152
153 Binary representation of integers:
154
155 - On little and big endian:
156 - Within a byte, high bits correspond to an integer high bits, and low bits
157 correspond to low bits.
158 - On little endian:
159 - Integer across multiple bytes are placed from the less significant to the
160 most significant.
161 - Consecutive integers are placed from lower bits to higher bits (even within
162 a byte).
163 - On big endian:
164 - Integer across multiple bytes are placed from the most significant to the
165 less significant.
166 - Consecutive integers are placed from higher bits to lower bits (even within
167 a byte).
168
169 This binary representation is derived from the bitfield implementation in GCC
170 for little and big endian. However, contrary to what GCC does, integers can
171 cross units boundaries (no padding is required). Padding can be explicitely
172 added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
173
174 Metadata representation:
175
176 integer {
177 signed = true OR false; /* default false */
178 byte_order = native OR network OR be OR le; /* default native */
179 size = value; /* value in bits, no default */
180 align = value; /* value in bits */
181 }
182
183 Example of type inheritance (creation of a uint32_t named type):
184
185 typealias integer {
186 size = 32;
187 signed = false;
188 align = 32;
189 } : uint32_t;
190
191 Definition of a named 5-bit signed bitfield:
192
193 typealias integer {
194 size = 5;
195 signed = true;
196 align = 1;
197 } : int5_t;
198
199 4.1.6 GNU/C bitfields
200
201 The GNU/C bitfields follow closely the integer representation, with a
202 particularity on alignment: if a bitfield cannot fit in the current unit, the
203 unit is padded and the bitfield starts at the following unit. The unit size is
204 defined by the size of the type "unit_type".
205
206 Metadata representation:
207
208 unit_type name:size:
209
210 As an example, the following structure declared in C compiled by GCC:
211
212 struct example {
213 short a:12;
214 short b:5;
215 };
216
217 The example structure is aligned on the largest element (short). The second
218 bitfield would be aligned on the next unit boundary, because it would not fit in
219 the current unit.
220
221 4.1.7 Floating point
222
223 The floating point values byte ordering is defined in the metadata.
224
225 Floating point values follow the IEEE 754-2008 standard interchange formats.
226 Description of the floating point values include the exponent and mantissa size
227 in bits. Some requirements are imposed on the floating point values:
228
229 - FLT_RADIX must be 2.
230 - mant_dig is the number of digits represented in the mantissa. It is specified
231 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
232 LDBL_MANT_DIG as defined by <float.h>.
233 - exp_dig is the number of digits represented in the exponent. Given that
234 mant_dig is one bit more than its actual size in bits (leading 1 is not
235 needed) and also given that the sign bit always takes one bit, exp_dig can be
236 specified as:
237
238 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
239 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
240 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
241
242 Metadata representation:
243
244 floating_point {
245 exp_dig = value;
246 mant_dig = value;
247 byte_order = native OR network OR be OR le;
248 }
249
250 Example of type inheritance:
251
252 typealias floating_point {
253 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
254 mant_dig = 24; /* FLT_MANT_DIG */
255 byte_order = native;
256 } : float;
257
258 TODO: define NaN, +inf, -inf behavior.
259
260 4.1.8 Enumerations
261
262 Enumerations are a mapping between an integer type and a table of strings. The
263 numerical representation of the enumeration follows the integer type specified
264 by the metadata. The enumeration mapping table is detailed in the enumeration
265 description within the metadata. The mapping table maps inclusive value ranges
266 (or single values) to strings. Instead of being limited to simple
267 "value -> string" mappings, these enumerations map
268 "[ start_value ... end_value ] -> string", which map inclusive ranges of
269 values to strings. An enumeration from the C language can be represented in
270 this format by having the same start_value and end_value for each element, which
271 is in fact a range of size 1. This single-value range is supported without
272 repeating the start and end values with the value = string declaration.
273
274 If a numeric value is encountered between < >, it represents the integer type
275 size used to hold the enumeration, in bits.
276
277 enum name <integer_type OR size> {
278 somestring = start_value1 ... end_value1,
279 "other string" = start_value2 ... end_value2,
280 yet_another_string, /* will be assigned to end_value2 + 1 */
281 "some other string" = value,
282 ...
283 };
284
285 If the values are omitted, the enumeration starts at 0 and increment of 1 for
286 each entry:
287
288 enum name <32> {
289 ZERO,
290 ONE,
291 TWO,
292 TEN = 10,
293 ELEVEN,
294 };
295
296 Overlapping ranges within a single enumeration are implementation defined.
297
298 A nameless enumeration can be declared as a field type or as part of a typedef:
299
300 enum <integer_type> {
301 ...
302 }
303
304
305 4.2 Compound types
306
307 Compound are aggregation of type declarations. Compound types include
308 structures, variant, arrays, sequences, and strings.
309
310 4.2.1 Structures
311
312 Structures are aligned on the largest alignment required by basic types
313 contained within the structure. (This follows the ISO/C standard for structures)
314
315 Metadata representation of a named structure:
316
317 struct name {
318 field_type field_name;
319 field_type field_name;
320 ...
321 };
322
323 Example:
324
325 struct example {
326 integer { /* Nameless type */
327 size = 16;
328 signed = true;
329 align = 16;
330 } first_field_name;
331 uint64_t second_field_name; /* Named type declared in the metadata */
332 };
333
334 The fields are placed in a sequence next to each other. They each possess a
335 field name, which is a unique identifier within the structure.
336
337 A nameless structure can be declared as a field type or as part of a typedef:
338
339 struct {
340 ...
341 }
342
343 4.2.2 Variants (Discriminated/Tagged Unions)
344
345 A CTF variant is a selection between different types. A CTF variant must
346 always be defined within the scope of a structure or within fields
347 contained within a structure (defined recursively). A "tag" enumeration
348 field must appear in either the same lexical scope, prior to the variant
349 field (in field declaration order), in an uppermost lexical scope (see
350 Section 7.2.1), or in an uppermost dynamic scope (see Section 7.2.2).
351 The type selection is indicated by the mapping from the enumeration
352 value to the string used as variant type selector. The field to use as
353 tag is specified by the "tag_field", specified between "< >" after the
354 "variant" keyword for unnamed variants, and after "variant name" for
355 named variants.
356
357 The alignment of the variant is the alignment of the type as selected by the tag
358 value for the specific instance of the variant. The alignment of the type
359 containing the variant is independent of the variant alignment. The size of the
360 variant is the size as selected by the tag value for the specific instance of
361 the variant.
362
363 A named variant declaration followed by its definition within a structure
364 declaration:
365
366 variant name {
367 field_type sel1;
368 field_type sel2;
369 field_type sel3;
370 ...
371 };
372
373 struct {
374 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
375 ...
376 variant name <tag_field> v;
377 }
378
379 An unnamed variant definition within a structure is expressed by the following
380 metadata:
381
382 struct {
383 enum <integer_type or size> { sel1, sel2, sel3, ... } tag_field;
384 ...
385 variant <tag_field> {
386 field_type sel1;
387 field_type sel2;
388 field_type sel3;
389 ...
390 } v;
391 }
392
393 Example of a named variant within a sequence that refers to a single tag field:
394
395 variant example {
396 uint32_t a;
397 uint64_t b;
398 short c;
399 };
400
401 struct {
402 enum <uint2_t> { a, b, c } choice;
403 variant example <choice> v[unsigned int];
404 }
405
406 Example of an unnamed variant:
407
408 struct {
409 enum <uint2_t> { a, b, c, d } choice;
410 /* Unrelated fields can be added between the variant and its tag */
411 int32_t somevalue;
412 variant <choice> {
413 uint32_t a;
414 uint64_t b;
415 short c;
416 struct {
417 unsigned int field1;
418 uint64_t field2;
419 } d;
420 } s;
421 }
422
423 Example of an unnamed variant within an array:
424
425 struct {
426 enum <uint2_t> { a, b, c } choice;
427 variant <choice> {
428 uint32_t a;
429 uint64_t b;
430 short c;
431 } v[10];
432 }
433
434 Example of a variant type definition within a structure, where the defined type
435 is then declared within an array of structures. This variant refers to a tag
436 located in an upper lexical scope. This example clearly shows that a variant
437 type definition referring to the tag "x" uses the closest preceding field from
438 the lexical scope of the type definition.
439
440 struct {
441 enum <uint2_t> { a, b, c, d } x;
442
443 typedef variant <x> { /*
444 * "x" refers to the preceding "x" enumeration in the
445 * lexical scope of the type definition.
446 */
447 uint32_t a;
448 uint64_t b;
449 short c;
450 } example_variant;
451
452 struct {
453 enum <int> { x, y, z } x; /* This enumeration is not used by "v". */
454 example_variant v; /*
455 * "v" uses the "enum <uint2_t> { a, b, c, d }"
456 * tag.
457 */
458 } a[10];
459 }
460
461 4.2.3 Arrays
462
463 Arrays are fixed-length. Their length is declared in the type declaration within
464 the metadata. They contain an array of "inner type" elements, which can refer to
465 any type not containing the type of the array being declared (no circular
466 dependency). The length is the number of elements in an array.
467
468 Metadata representation of a named array:
469
470 typedef elem_type name[length];
471
472 A nameless array can be declared as a field type within a structure, e.g.:
473
474 uint8_t field_name[10];
475
476
477 4.2.4 Sequences
478
479 Sequences are dynamically-sized arrays. They start with an integer that specify
480 the length of the sequence, followed by an array of "inner type" elements.
481 The length is the number of elements in the sequence.
482
483 Metadata representation for a named sequence:
484
485 typedef elem_type name[length_type];
486
487 A nameless sequence can be declared as a field type, e.g.:
488
489 long field_name[int];
490
491 The length type follows the integer types specifications, and the sequence
492 elements follow the "array" specifications.
493
494 4.2.5 Strings
495
496 Strings are an array of bytes of variable size and are terminated by a '\0'
497 "NULL" character. Their encoding is described in the metadata. In absence of
498 encoding attribute information, the default encoding is UTF-8.
499
500 Metadata representation of a named string type:
501
502 typealias string {
503 encoding = UTF8 OR ASCII;
504 } : name;
505
506 A nameless string type can be declared as a field type:
507
508 string field_name; /* Use default UTF8 encoding */
509
510 5. Event Packet Header
511
512 The event packet header consists of two part: one is mandatory and have a fixed
513 layout. The second part, the "event packet context", has its layout described in
514 the metadata.
515
516 - Aligned on page size. Fixed size. Fields either aligned or packed (depending
517 on the architecture preference).
518 No padding at the end of the event packet header. Native architecture byte
519 ordering.
520
521 Fixed layout (event packet header):
522
523 - Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
524 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
525 representation. Used to distinguish between big and little endian traces (this
526 information is determined by knowing the endianness of the architecture
527 reading the trace and comparing the magic number against its value and the
528 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
529 description language described in this document. Different magic numbers
530 should be used for other metadata description languages.
531 - Trace UUID, used to ensure the event packet match the metadata used.
532 (note: we cannot use a metadata checksum because metadata can be appended to
533 while tracing is active)
534 - Stream ID, used as reference to stream description in metadata.
535
536 Metadata-defined layout (event packet context):
537
538 - Event packet content size (in bytes).
539 - Event packet size (in bytes, includes padding).
540 - Event packet content checksum (optional). Checksum excludes the event packet
541 header.
542 - Per-stream event packet sequence count (to deal with UDP packet loss). The
543 number of significant sequence counter bits should also be present, so
544 wrap-arounds are deal with correctly.
545 - Timestamp at the beginning and timestamp at the end of the event packet.
546 Both timestamps are written in the packet header, but sampled respectively
547 while (or before) writing the first event and while (or after) writing the
548 last event in the packet. The inclusive range between these timestamps should
549 include all event timestamps assigned to events contained within the packet.
550 - Events discarded count
551 - Snapshot of a per-stream free-running counter, counting the number of
552 events discarded that were supposed to be written in the stream prior to
553 the first event in the event packet.
554 * Note: producer-consumer buffer full condition should fill the current
555 event packet with padding so we know exactly where events have been
556 discarded.
557 - Lossless compression scheme used for the event packet content. Applied
558 directly to raw data. New types of compression can be added in following
559 versions of the format.
560 0: no compression scheme
561 1: bzip2
562 2: gzip
563 3: xz
564 - Cypher used for the event packet content. Applied after compression.
565 0: no encryption
566 1: AES
567 - Checksum scheme used for the event packet content. Applied after encryption.
568 0: no checksum
569 1: md5
570 2: sha1
571 3: crc32
572
573 5.1 Event Packet Header Fixed Layout Description
574
575 struct event_packet_header {
576 uint32_t magic;
577 uint8_t trace_uuid[16];
578 uint32_t stream_id;
579 };
580
581 5.2 Event Packet Context Description
582
583 Event packet context example. These are declared within the stream declaration
584 in the metadata. All these fields are optional except for "content_size" and
585 "packet_size", which must be present in the context.
586
587 An example event packet context type:
588
589 struct event_packet_context {
590 uint64_t timestamp_begin;
591 uint64_t timestamp_end;
592 uint32_t checksum;
593 uint32_t stream_packet_count;
594 uint32_t events_discarded;
595 uint32_t cpu_id;
596 uint32_t/uint16_t content_size;
597 uint32_t/uint16_t packet_size;
598 uint8_t stream_packet_count_bits; /* Significant counter bits */
599 uint8_t compression_scheme;
600 uint8_t encryption_scheme;
601 uint8_t checksum_scheme;
602 };
603
604
605 6. Event Structure
606
607 The overall structure of an event is:
608
609 1 - Stream Packet Context (as specified by the stream metadata)
610 2 - Event Header (as specified by the stream metadata)
611 3 - Stream Event Context (as specified by the stream metadata)
612 4 - Event Context (as specified by the event metadata)
613 5 - Event Payload (as specified by the event metadata)
614
615 This structure defines an implicit dynamic scoping, where variants
616 located in inner structures (those with a higher number in the listing
617 above) can refer to the fields of outer structures (with lower number in
618 the listing above). See Section 7.2 Metadata Scopes for more detail.
619
620 6.1 Event Header
621
622 Event headers can be described within the metadata. We hereby propose, as an
623 example, two types of events headers. Type 1 accommodates streams with less than
624 31 event IDs. Type 2 accommodates streams with 31 or more event IDs.
625
626 One major factor can vary between streams: the number of event IDs assigned to
627 a stream. Luckily, this information tends to stay relatively constant (modulo
628 event registration while trace is being recorded), so we can specify different
629 representations for streams containing few event IDs and streams containing
630 many event IDs, so we end up representing the event ID and timestamp as densely
631 as possible in each case.
632
633 The header is extended in the rare occasions where the information cannot be
634 represented in the ranges available in the standard event header. They are also
635 used in the rare occasions where the data required for a field could not be
636 collected: the flag corresponding to the missing field within the missing_fields
637 array is then set to 1.
638
639 Types uintX_t represent an X-bit unsigned integer.
640
641
642 6.1.1 Type 1 - Few event IDs
643
644 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
645 preference).
646 - Native architecture byte ordering.
647 - For "compact" selection
648 - Fixed size: 32 bits.
649 - For "extended" selection
650 - Size depends on the architecture and variant alignment.
651
652 struct event_header_1 {
653 /*
654 * id: range: 0 - 30.
655 * id 31 is reserved to indicate an extended header.
656 */
657 enum <uint5_t> { compact = 0 ... 30, extended = 31 } id;
658 variant <id> {
659 struct {
660 uint27_t timestamp;
661 } compact;
662 struct {
663 uint32_t id; /* 32-bit event IDs */
664 uint64_t timestamp; /* 64-bit timestamps */
665 } extended;
666 } v;
667 };
668
669
670 6.1.2 Type 2 - Many event IDs
671
672 - Aligned on 16-bit (or 8-bit if byte-packed, depending on the architecture
673 preference).
674 - Native architecture byte ordering.
675 - For "compact" selection
676 - Size depends on the architecture and variant alignment.
677 - For "extended" selection
678 - Size depends on the architecture and variant alignment.
679
680 struct event_header_2 {
681 /*
682 * id: range: 0 - 65534.
683 * id 65535 is reserved to indicate an extended header.
684 */
685 enum <uint16_t> { compact = 0 ... 65534, extended = 65535 } id;
686 variant <id> {
687 struct {
688 uint32_t timestamp;
689 } compact;
690 struct {
691 uint32_t id; /* 32-bit event IDs */
692 uint64_t timestamp; /* 64-bit timestamps */
693 } extended;
694 } v;
695 };
696
697
698 6.2 Event Context
699
700 The event context contains information relative to the current event. The choice
701 and meaning of this information is specified by the metadata "stream" and
702 "event" information. The "stream" context is applied to all events within the
703 stream. The "stream" context structure follows the event header. The "event"
704 context is applied to specific events. Its structure follows the "stream"
705 context stucture.
706
707 An example of stream-level event context is to save the event payload size with
708 each event, or to save the current PID with each event. These are declared
709 within the stream declaration within the metadata:
710
711 stream {
712 ...
713 event {
714 ...
715 context := struct {
716 uint pid;
717 uint16_t payload_size;
718 };
719 }
720 };
721
722 An example of event-specific event context is to declare a bitmap of missing
723 fields, only appended after the stream event context if the extended event
724 header is selected. NR_FIELDS is the number of fields within the event (a
725 numeric value).
726
727 event {
728 context = struct {
729 variant <id> {
730 struct { } compact;
731 struct {
732 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
733 } extended;
734 } v;
735 };
736 ...
737 }
738
739 6.3 Event Payload
740
741 An event payload contains fields specific to a given event type. The fields
742 belonging to an event type are described in the event-specific metadata
743 within a structure type.
744
745 6.3.1 Padding
746
747 No padding at the end of the event payload. This differs from the ISO/C standard
748 for structures, but follows the CTF standard for structures. In a trace, even
749 though it makes sense to align the beginning of a structure, it really makes no
750 sense to add padding at the end of the structure, because structures are usually
751 not followed by a structure of the same type.
752
753 This trick can be done by adding a zero-length "end" field at the end of the C
754 structures, and by using the offset of this field rather than using sizeof()
755 when calculating the size of a structure (see Appendix "A. Helper macros").
756
757 6.3.2 Alignment
758
759 The event payload is aligned on the largest alignment required by types
760 contained within the payload. (This follows the ISO/C standard for structures)
761
762
763 7. Metadata
764
765 The meta-data is located in a stream identified by its name: "metadata".
766 It is made of "event packets", which each start with an event packet
767 header. The event type within the metadata stream have no event header
768 nor event context. Each event only contains a null-terminated "string"
769 payload, which is a metadata description entry. The events are packed
770 one next to another. Each event packet start with an event packet
771 header, which contains, amongst other fields, the magic number and trace
772 UUID. In the event packet header, the trace UUID is represented as an
773 array of bytes. Within the string-based metadata description, the trace
774 UUID is represented as a string of hexadecimal digits and dashes "-".
775
776 The metadata can be parsed by reading through the metadata strings,
777 skipping null-characters. Type names are made of a single identifier,
778 and can be surrounded by prefix/postfix. Text contained within "/*" and
779 "*/", as well as within "//" and end of line, are treated as comments.
780 Boolean values can be represented as true, TRUE, or 1 for true, and
781 false, FALSE, or 0 for false.
782
783
784 7.1 Declaration vs Definition
785
786 A declaration associates a layout to a type, without specifying where
787 this type is located in the event structure hierarchy (see Section 6).
788 This therefore includes typedef, typealias, as well as all type
789 specifiers. In certain circumstances (typedef, structure field and
790 variant field), a declaration is followed by a declarator, which specify
791 the newly defined type name (for typedef), or the field name (for
792 declarations located within structure and variants). Array and sequence,
793 declared with square brackets ("[" "]"), are part of the declarator,
794 similarly to C99. The enumeration type specifier and variant tag name
795 (both specified with "<" ">") are part of the type specifier.
796
797 A definition associates a type to a location in the event structure
798 hierarchy (see Section 6). This association is denoted by ":=", as shown
799 in Section 7.3.
800
801
802 7.2 Metadata Scopes
803
804 CTF metadata uses two different types of scoping: a lexical scope is
805 used for declarations and type definitions, and a dynamic scope is used
806 for variants references to tag fields.
807
808 7.2.1 Lexical Scope
809
810 Each of "trace", "stream", "event", "struct" and "variant" have their own
811 nestable declaration scope, within which types can be declared using "typedef"
812 and "typealias". A root declaration scope also contains all declarations
813 located outside of any of the aforementioned declarations. An inner
814 declaration scope can refer to type declared within its container
815 lexical scope prior to the inner declaration scope. Redefinition of a
816 typedef or typealias is not valid, although hiding an upper scope
817 typedef or typealias is allowed within a sub-scope.
818
819 7.2.2 Dynamic Scope
820
821 A dynamic scope consists in the lexical scope augmented with the
822 implicit event structure definition hierarchy presented at Section 6.
823 The dynamic scope is only used for variant tag definitions. It is used
824 at definition time to look up the location of the tag field associated
825 with a variant.
826
827 Therefore, variants in lower levels in the dynamic scope (e.g. event
828 context) can refer to a tag field located in upper levels (e.g. in the
829 event header) by specifying, in this case, the associated tag with
830 <header.field_name>. This allows, for instance, the event context to
831 define a variant referring to the "id" field of the event header as
832 selector.
833
834 The target dynamic scope must be specified explicitly when referring to
835 a field outside of the local static scope. The dynamic scope prefixes
836 are thus:
837
838 - Stream Packet Context: <stream.packet.context. >,
839 - Event Header: <stream.event.header. >,
840 - Stream Event Context: <stream.event.context. >,
841 - Event Context: <event.context. >,
842 - Event Payload: <event.fields. >.
843
844 Multiple declarations of the same field name within a single scope is
845 not valid. It is however valid to re-use the same field name in
846 different scopes. There is no possible conflict, because the dynamic
847 scope must be specified when a variant refers to a tag field located in
848 a different dynamic scope.
849
850 The information available in the dynamic scopes can be thought of as the
851 current tracing context. At trace production, information about the
852 current context is saved into the specified scope field levels. At trace
853 consumption, for each event, the current trace context is therefore
854 readable by accessing the upper dynamic scopes.
855
856
857 7.3 Metadata Examples
858
859 The grammar representing the CTF metadata is presented in
860 Appendix C. CTF Metadata Grammar. This section presents a rather ligher
861 reading that consists in examples of CTF metadata, with template values:
862
863 trace {
864 major = value; /* Trace format version */
865 minor = value;
866 uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */
867 word_size = value;
868 };
869
870 stream {
871 id = stream_id;
872 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
873 event.header := event_header_1 OR event_header_2;
874 event.context := struct {
875 ...
876 };
877 packet.context := struct {
878 ...
879 };
880 };
881
882 event {
883 name = event_name;
884 id = value; /* Numeric identifier within the stream */
885 stream = stream_id;
886 context := struct {
887 ...
888 };
889 fields := struct {
890 ...
891 };
892 };
893
894 /* More detail on types in section 4. Types */
895
896 /*
897 * Named types:
898 *
899 * Type declarations behave similarly to the C standard.
900 */
901
902 typedef aliased_type_prefix aliased_type new_type aliased_type_postfix;
903
904 /* e.g.: typedef struct example new_type_name[10]; */
905
906 /*
907 * typealias
908 *
909 * The "typealias" declaration can be used to give a name (including
910 * prefix/postfix) to a type. It should also be used to map basic C types
911 * (float, int, unsigned long, ...) to a CTF type. Typealias is a superset of
912 * "typedef": it also allows assignment of a simple variable identifier to a
913 * type.
914 */
915
916 typealias type_class {
917 ...
918 } : new_type_prefix new_type new_type_postfix;
919
920 /*
921 * e.g.:
922 * typealias integer {
923 * size = 32;
924 * align = 32;
925 * signed = false;
926 * } : struct page *;
927 *
928 * typealias integer {
929 * size = 32;
930 * align = 32;
931 * signed = true;
932 * } : int;
933 */
934
935 struct name {
936 ...
937 };
938
939 variant name {
940 ...
941 };
942
943 enum name <integer_type or size> {
944 ...
945 };
946
947
948 /*
949 * Unnamed types, contained within compound type fields, typedef or typealias.
950 */
951
952 struct {
953 ...
954 }
955
956 variant {
957 ...
958 }
959
960 enum <integer_type or size> {
961 ...
962 }
963
964 typedef type new_type[length];
965
966 struct {
967 type field_name[length];
968 }
969
970 typedef type new_type[length_type];
971
972 struct {
973 type field_name[length_type];
974 }
975
976 integer {
977 ...
978 }
979
980 floating_point {
981 ...
982 }
983
984 struct {
985 integer_type field_name:size; /* GNU/C bitfield */
986 }
987
988 struct {
989 string field_name;
990 }
991
992
993 A. Helper macros
994
995 The two following macros keep track of the size of a GNU/C structure without
996 padding at the end by placing HEADER_END as the last field. A one byte end field
997 is used for C90 compatibility (C99 flexible arrays could be used here). Note
998 that this does not affect the effective structure size, which should always be
999 calculated with the header_sizeof() helper.
1000
1001 #define HEADER_END char end_field
1002 #define header_sizeof(type) offsetof(typeof(type), end_field)
1003
1004
1005 B. Stream Header Rationale
1006
1007 An event stream is divided in contiguous event packets of variable size. These
1008 subdivisions allow the trace analyzer to perform a fast binary search by time
1009 within the stream (typically requiring to index only the event packet headers)
1010 without reading the whole stream. These subdivisions have a variable size to
1011 eliminate the need to transfer the event packet padding when partially filled
1012 event packets must be sent when streaming a trace for live viewing/analysis.
1013 An event packet can contain a certain amount of padding at the end. Dividing
1014 streams into event packets is also useful for network streaming over UDP and
1015 flight recorder mode tracing (a whole event packet can be swapped out of the
1016 buffer atomically for reading).
1017
1018 The stream header is repeated at the beginning of each event packet to allow
1019 flexibility in terms of:
1020
1021 - streaming support,
1022 - allowing arbitrary buffers to be discarded without making the trace
1023 unreadable,
1024 - allow UDP packet loss handling by either dealing with missing event packet
1025 or asking for re-transmission.
1026 - transparently support flight recorder mode,
1027 - transparently support crash dump.
1028
1029 The event stream header will therefore be referred to as the "event packet
1030 header" throughout the rest of this document.
1031
1032 C. CTF Metadata Grammar
1033
1034 /*
1035 * Common Trace Format (CTF) Metadata Grammar.
1036 *
1037 * Inspired from the C99 grammar:
1038 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
1039 *
1040 * Specialized for CTF needs by including only constant and declarations from
1041 * C99 (excluding function declarations), and by adding support for variants,
1042 * sequences and CTF-specific specifiers.
1043 */
1044
1045 1) Lexical grammar
1046
1047 1.1) Lexical elements
1048
1049 token:
1050 keyword
1051 identifier
1052 constant
1053 string-literal
1054 punctuator
1055
1056 1.2) Keywords
1057
1058 keyword: is one of
1059
1060 const
1061 char
1062 double
1063 enum
1064 event
1065 floating_point
1066 float
1067 integer
1068 int
1069 long
1070 short
1071 signed
1072 stream
1073 string
1074 struct
1075 trace
1076 typealias
1077 typedef
1078 unsigned
1079 variant
1080 void
1081 _Bool
1082 _Complex
1083 _Imaginary
1084
1085
1086 1.3) Identifiers
1087
1088 identifier:
1089 identifier-nondigit
1090 identifier identifier-nondigit
1091 identifier digit
1092
1093 identifier-nondigit:
1094 nondigit
1095 universal-character-name
1096 any other implementation-defined characters
1097
1098 nondigit:
1099 _
1100 [a-zA-Z] /* regular expression */
1101
1102 digit:
1103 [0-9] /* regular expression */
1104
1105 1.4) Universal character names
1106
1107 universal-character-name:
1108 \u hex-quad
1109 \U hex-quad hex-quad
1110
1111 hex-quad:
1112 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
1113
1114 1.5) Constants
1115
1116 constant:
1117 integer-constant
1118 enumeration-constant
1119 character-constant
1120
1121 integer-constant:
1122 decimal-constant integer-suffix-opt
1123 octal-constant integer-suffix-opt
1124 hexadecimal-constant integer-suffix-opt
1125
1126 decimal-constant:
1127 nonzero-digit
1128 decimal-constant digit
1129
1130 octal-constant:
1131 0
1132 octal-constant octal-digit
1133
1134 hexadecimal-constant:
1135 hexadecimal-prefix hexadecimal-digit
1136 hexadecimal-constant hexadecimal-digit
1137
1138 hexadecimal-prefix:
1139 0x
1140 0X
1141
1142 nonzero-digit:
1143 [1-9]
1144
1145 integer-suffix:
1146 unsigned-suffix long-suffix-opt
1147 unsigned-suffix long-long-suffix
1148 long-suffix unsigned-suffix-opt
1149 long-long-suffix unsigned-suffix-opt
1150
1151 unsigned-suffix:
1152 u
1153 U
1154
1155 long-suffix:
1156 l
1157 L
1158
1159 long-long-suffix:
1160 ll
1161 LL
1162
1163 digit-sequence:
1164 digit
1165 digit-sequence digit
1166
1167 hexadecimal-digit-sequence:
1168 hexadecimal-digit
1169 hexadecimal-digit-sequence hexadecimal-digit
1170
1171 enumeration-constant:
1172 identifier
1173 string-literal
1174
1175 character-constant:
1176 ' c-char-sequence '
1177 L' c-char-sequence '
1178
1179 c-char-sequence:
1180 c-char
1181 c-char-sequence c-char
1182
1183 c-char:
1184 any member of source charset except single-quote ('), backslash
1185 (\), or new-line character.
1186 escape-sequence
1187
1188 escape-sequence:
1189 simple-escape-sequence
1190 octal-escape-sequence
1191 hexadecimal-escape-sequence
1192 universal-character-name
1193
1194 simple-escape-sequence: one of
1195 \' \" \? \\ \a \b \f \n \r \t \v
1196
1197 octal-escape-sequence:
1198 \ octal-digit
1199 \ octal-digit octal-digit
1200 \ octal-digit octal-digit octal-digit
1201
1202 hexadecimal-escape-sequence:
1203 \x hexadecimal-digit
1204 hexadecimal-escape-sequence hexadecimal-digit
1205
1206 1.6) String literals
1207
1208 string-literal:
1209 " s-char-sequence-opt "
1210 L" s-char-sequence-opt "
1211
1212 s-char-sequence:
1213 s-char
1214 s-char-sequence s-char
1215
1216 s-char:
1217 any member of source charset except double-quote ("), backslash
1218 (\), or new-line character.
1219 escape-sequence
1220
1221 1.7) Punctuators
1222
1223 punctuator: one of
1224 [ ] ( ) { } . -> * + - < > : ; ... = ,
1225
1226
1227 2) Phrase structure grammar
1228
1229 primary-expression:
1230 identifier
1231 constant
1232 string-literal
1233 ( unary-expression )
1234
1235 postfix-expression:
1236 primary-expression
1237 postfix-expression [ unary-expression ]
1238 postfix-expression . identifier
1239 postfix-expressoin -> identifier
1240
1241 unary-expression:
1242 postfix-expression
1243 unary-operator postfix-expression
1244
1245 unary-operator: one of
1246 + -
1247
1248 assignment-operator:
1249 =
1250
1251 type-assignment-operator:
1252 :=
1253
1254 constant-expression:
1255 unary-expression
1256
1257 constant-expression-range:
1258 constant-expression ... constant-expression
1259
1260 2.2) Declarations:
1261
1262 declaration:
1263 declaration-specifiers declarator-list-opt ;
1264 ctf-specifier ;
1265
1266 declaration-specifiers:
1267 storage-class-specifier declaration-specifiers-opt
1268 type-specifier declaration-specifiers-opt
1269 type-qualifier declaration-specifiers-opt
1270
1271 declarator-list:
1272 declarator
1273 declarator-list , declarator
1274
1275 abstract-declarator-list:
1276 abstract-declarator
1277 abstract-declarator-list , abstract-declarator
1278
1279 storage-class-specifier:
1280 typedef
1281
1282 type-specifier:
1283 void
1284 char
1285 short
1286 int
1287 long
1288 float
1289 double
1290 signed
1291 unsigned
1292 _Bool
1293 _Complex
1294 _Imaginary
1295 struct-specifier
1296 variant-specifier
1297 enum-specifier
1298 typedef-name
1299 ctf-type-specifier
1300
1301 struct-specifier:
1302 struct identifier-opt { struct-or-variant-declaration-list-opt }
1303 struct identifier
1304
1305 struct-or-variant-declaration-list:
1306 struct-or-variant-declaration
1307 struct-or-variant-declaration-list struct-or-variant-declaration
1308
1309 struct-or-variant-declaration:
1310 specifier-qualifier-list struct-or-variant-declarator-list ;
1311 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
1312 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1313 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1314
1315 specifier-qualifier-list:
1316 type-specifier specifier-qualifier-list-opt
1317 type-qualifier specifier-qualifier-list-opt
1318
1319 struct-or-variant-declarator-list:
1320 struct-or-variant-declarator
1321 struct-or-variant-declarator-list , struct-or-variant-declarator
1322
1323 struct-or-variant-declarator:
1324 declarator
1325 declarator-opt : constant-expression
1326
1327 variant-specifier:
1328 variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
1329 variant identifier variant-tag
1330
1331 variant-tag:
1332 < identifier >
1333
1334 enum-specifier:
1335 enum identifier-opt { enumerator-list }
1336 enum identifier-opt { enumerator-list , }
1337 enum identifier
1338 enum identifier-opt < declaration-specifiers > { enumerator-list }
1339 enum identifier-opt < declaration-specifiers > { enumerator-list , }
1340 enum identifier < declaration-specifiers >
1341 enum identifier-opt < integer-constant > { enumerator-list }
1342 enum identifier-opt < integer-constant > { enumerator-list , }
1343 enum identifier < integer-constant >
1344
1345 enumerator-list:
1346 enumerator
1347 enumerator-list , enumerator
1348
1349 enumerator:
1350 enumeration-constant
1351 enumeration-constant = constant-expression
1352 enumeration-constant = constant-expression-range
1353
1354 type-qualifier:
1355 const
1356
1357 declarator:
1358 pointer-opt direct-declarator
1359
1360 direct-declarator:
1361 identifier
1362 ( declarator )
1363 direct-declarator [ type-specifier ]
1364 direct-declarator [ constant-expression ]
1365
1366 abstract-declarator:
1367 pointer-opt direct-abstract-declarator
1368
1369 direct-abstract-declarator:
1370 identifier-opt
1371 ( abstract-declarator )
1372 direct-abstract-declarator [ type-specifier ]
1373 direct-abstract-declarator [ constant-expression ]
1374 direct-abstract-declarator [ ]
1375
1376 pointer:
1377 * type-qualifier-list-opt
1378 * type-qualifier-list-opt pointer
1379
1380 type-qualifier-list:
1381 type-qualifier
1382 type-qualifier-list type-qualifier
1383
1384 typedef-name:
1385 identifier
1386
1387 2.3) CTF-specific declarations
1388
1389 ctf-specifier:
1390 event { ctf-assignment-expression-list-opt }
1391 stream { ctf-assignment-expression-list-opt }
1392 trace { ctf-assignment-expression-list-opt }
1393 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list ;
1394 typealias declaration-specifiers abstract-declarator-list : declarator-list ;
1395
1396 ctf-type-specifier:
1397 floating_point { ctf-assignment-expression-list-opt }
1398 integer { ctf-assignment-expression-list-opt }
1399 string { ctf-assignment-expression-list-opt }
1400
1401 ctf-assignment-expression-list:
1402 ctf-assignment-expression
1403 ctf-assignment-expression-list ; ctf-assignment-expression
1404
1405 ctf-assignment-expression:
1406 unary-expression assignment-operator unary-expression
1407 unary-expression type-assignment-operator type-specifier
1408 declaration-specifiers storage-class-specifier declaration-specifiers declarator-list
1409 typealias declaration-specifiers abstract-declarator-list : declaration-specifiers abstract-declarator-list
1410 typealias declaration-specifiers abstract-declarator-list : declarator-list
This page took 0.097145 seconds and 4 git commands to generate.